• NSA and GCHQ unlock encryption used to protect emails, banking and medical records• $250m-a-year US program works covertly with tech companies to insert weaknesses into products• Security experts say programs 'undermine the fabric of the internet'

In the second part of an exclusive interview with Glenn Greenwald and Laura Poitras, former NSA contractor Edward Snowden contemplates the reaction from the US government to his revelations of top secret documents regarding its spying operations on domestic and foreign internet traffic, email and phone use